1. Field of the Invention
The present invention relates to a coordinate input apparatus, a coordinate inputting method, an information display system and a storage medium used for a large information display system. More particularly, it mainly relates to a coordinate input apparatus that is used for controlling a computer externally connected and writing characters and graphics by inputting coordinates directly in the screen of a large display with a designation device.
2. Related Background Art
In recent years, large-screen displays are being not only improved in brightness but also increased in scale of screens and resolution. For coordinate input apparatuses that are used in these devices, pen-shaped types are used, and cordless types are used because of large input areas, and for this type of devices, devices that use ring-shaped Change Coupled Device (CCD) as an optical/electrical conversion element (hereinafter referred to as a ring CCD), have high resistance to external random lights, and are compact and inexpensive are proposed, as described in Japanese Patent Application Laid-open No. 10-019506.
These coordinate input apparatuses using the ring CCD blink input lights and use a differential between the input lights during lit conditions and the input lights during unlit conditions to detect the input lights. For this reason, they are adapted for detecting timings during lit conditions and during unlit conditions and performing cordless input. In recent years, the number of pixels of the CCD has been increased, and coordinate input apparatuses with the larger numbers of bits have been devised. The resolution is improved as the number of bits is increased, but time required for reading data is prolonged accordingly.
Also, for the number of pixels needed to calculate a coordinate, the whole width of CCD pixels are not required and only the data of inputted portions are necessary, thus causing a loss of time during read of unnecessary pixel data. Furthermore, if long time is required for detection of input lights, the speed of input is affected, resulting in loss of agility in terms of usage.